A preload applied to a linear guideway included in a machine tool is gradually reduced due to wear and tear in use. When reduction of the preload reaches a certain amount, the linear guideway has to be replaced by a new one.
A conventional method for estimating a variation in the preload requires the linear guideway to be removed from the machine tool before the preload can be measured by a measuring tool. To monitor the variation in the preload, the preload has to be measured repeatedly, and hence the linear guideway has to be removed from the machine tool regularly. The conventional method is consequently time-consuming and inconvenient.